Crop yield response to water - Cra

Figure 10Response of marketable fruit yield (>70 mm) and revenue of Golden Delicious apple toirrigation rates (average seasonal reference ET o K c ) at various crop levels (1 250 tree/ha).Different irrigation rates were applied from mid-June to harvest – K c values were 0.44, 0.65,0.84, 1.01, and 1.19; seasonal ET o (1/5-1/11) was 1 172 mm.91 182 286 424Crop yield >70 mm (tonne/ha)10080604020Fruit/treeRevenue *1 000 in US$/ha1401201008060402000.0 0.2 0.4 0.6 0.8Average seasonal crop coefficient00.0 0.2 0.4 0.6 0.8Average seasonal crop coefficientSuggested RDI RegimesGiven the growth patterns of the apple, and the sensitivity of fruit size to water deficits, itappears that only mild water deficits may be applied to this crop, when grown for fresh market,without impacting negatively on farmers’ income. However, RDI has some positive effects onquality that should be exploited, in particular in water scarcity situations. The objective of appleirrigation management under suboptimal water allocation would be to minimize damage andmaximize irrigation water productivity. If a small reduction in supply is considered, it should occurpreferably during the postharvest period. In common varieties that are harvested in September(Northern Hemisphere) it leaves some period of irrigation up to the start of leaf senescence, aperiod that will be shorter with increasing latitude. In water shortage conditions one can skipthe postharvest irrigation for common varieties but that should not be done in early maturingvarieties that have long postharvest period. If water shortages exceed the level equivalent tothe amount used for postharvest irrigation, growers should apply the deficit on a continuousbasis after the early fruit growth period (avoid stress in the first 30 to 60 days after fruit set,depending on variety), and adjust the crop load by thinning to ensure that the remaining fruitwill reach commercial size. A recommendation on irrigation for different water allocations andoptimal crop loads for production in warm climates is presented in Table 2.It is important to monitor soil or tree water status when applying RDI (see Chapter 4). Climatecontrol for apple (frost protection and/or cooling for sunburn protection or to enhance redcolour in warm areas) is carried out using sprinkler irrigation and its use, in the case of cooling,may disrupt the RDI programme. Evaporative cooling reduces actual ET on the order of 20percent, but total seasonal irrigation water requirements would be much higher than the fullorchard ET c , as calculated in Chapter 4.APPLE 343